NATURAL HISTORY. 



603 



tree neath, which shrub rises to the 

 height of 18 or 20 feet. Some of the 

 stems are as thick as the arm of a 

 man, joined together in bunches or 

 tufts like the common heath. The 

 form of this forest is oblong ; it co- 

 vers the flank of those hills which I 

 have already denominated the cen- 

 tral chain from their summit to half 

 their elevation from the plain. — 

 The soil here is deep, and formed 

 of decomposed lava, small ash, and 

 pumice. I examined several chan- 

 nels in the strata or ravines worn 

 by the rains, and there was no ap- 

 pearance of any other rock. Leav- 

 ing this forest, the track passes over 

 a series of green hills which we 

 traversed in about two hours, and 

 at last halted to water our mules at 

 a spot called el barranco delpino de 

 la meruenda,viheTe there is a small 

 spring of bad and brackish water 

 issuing from a lava rock. The 

 ravine is of considerable depth. 

 After the vegetable earth, which is 

 two or three feet deep, a layer of 

 tufa succeeds, which is followed by 

 a lava of a greyisli-blue colour, 30 

 or 40 feet in depth. It is compact, 

 contains olivine, and the strata lap 

 over each other, but show no ap- 

 pearance of columnar formation. 

 The range of green hills extends a 

 mile or two further, the soil shallow- 

 ing by degrees, more lava and scoria 

 showing themselves on the surface, 

 the ravines or channels, worn by 

 the rains, becoming more common, 

 the trees and shrubs gradually 

 dwindling in size, and of them ail 

 the Spanish broom alone at length 

 covers the ground. Leaving be- 

 hind us this range of green hills, 

 the track, still ascending, leads, for 

 several hours, across a steep and 

 difficult mass of lava rock, broken 

 here and there into strange and 



fantastic forms, worn into deep ra- 

 vines, and scantily covered in places 

 by a thin layer of yellow pumice. 

 The surface of the country, for miles 

 and miles around, is of this one 

 continuous stream of lava ; the - 

 rents or ravines of which seem to 

 be formed partly by the torrents 

 from the hills flowing for so many- 

 ages, and partly from that tendency, 

 characteristic of a lava current, to 

 keep itself up in embankments, 

 and in its cooling process to open 

 out into those hollows whicli I have 

 uniformly found in every eruption 

 of lava that I have had an oppor- . 

 tunity of examining. This lava is 

 cellular beyond any 1 have ever 

 seen, is of a clayey earthy porphy- 

 ritic composition, and contains few 

 if any, pieces of olivine, though 

 here and there feldspar in a semi- 

 crystallised form. As we proceed- 

 ed on our road, the hills on our left, 

 though broken at times in deep ra- 

 vines, gradually rose in height till 

 the summits were lost in those of 

 the central chain, while on our 

 right we were rapidly gaining an 

 elevation above the lower range of 

 the peak. This range forms one 

 flank of the plain or valley of Oro- 

 tava, stretching from south-east to 

 north-west, and is broken into 

 steep precipices, cut down in some 

 places perpendicular to the hori- 

 zon, and called las Horcas : it joins 

 the central chain at the high ele- 

 vation of the pumice plains, sweeps 

 down the side of the valley, and 

 forms a headland near 200 feet 

 high, projecting into the sea, some 

 miles from Orotava ; we traversed 

 this country an hour or two, till 

 we reached the point of intersec- 

 tion of las Horcas with the plains 

 of pumice. On the road are seve- 

 ral small conical hills or mouths of 



